Typically, a light emitting diode (LED) emits light into a full hemisphere. For some applications, such as for display lighting or general room lighting, such an output can be desirable. However, for other applications, such as for a flashlight or a vehicular headlight, a more focused output is required.
To provide a narrower output light distribution angle, the light output from the LED often is condensed. A variety of devices have been developed to condense light from an LED, such as devices that utilize a parabolic reflector. Unfortunately, these prior devices have a number of drawbacks including being expensive to produce, physically large, inefficient, and unable to condense all of the light into a narrow output emission profile.
An alternate prior art method of condensing light from a source is shown in FIG. 1. This prior-art optical element has an input surface 4, onto which source 14 is located, an outer TIRing surface 1, and a lens-shaped output surface 2 through which all the light must exit. Light rays, such as 6 and 7, that propagate directly from the source 14 to the output surface 2 exit the output surface 2 in a direction that is substantially parallel to the optical axis A-A of the condensing element. The prescription of the lens-shaped output surface 2 is designed for this purpose.
Unfortunately not all of the light that exits the source 14 is directly incident onto the output surface 2. For example, light ray 8 exits the source 14 at a highly divergent angle and becomes incident on the outer surface 1. Light ray 8 then undergoes TIR at the outer surface 1, and then is incident on the output surface 2. Light ray 8 then refracts and exits through outer surface 2, and is directed in a direction that is not substantially parallel to the optical axis A-A. Light ray 8 therefore is not well condensed, and detracts from the overall performance of the condensing optical element. In this way, most prior art condensing optical elements suffer from poor light-condensing efficiency.